The present invention relates to a process for the catalytic treatment of polysilazanes and, more particulary, to the catalytic treatment of polyorganosilazanes and/or polyorgano(disilyl) silazanes with a catalyst system comprising an ionic inorganic salt and a complexing compound.
Organopolysilazanes are well-known products that occur in the form of monomers, oligomers, ring or linear polymers, and resinous polymers. These organopolysilazanes can be prepared using a wide variety of methods from a wide range of starting materials.
These organopolysilazanes can be, in particular, shaped and pyrolyzed in the form of Si.sub.3 N.sub.4 SiC or their mixtures. Silicon nitride can also be prepared by the reaction of chlorosilanes, such as SiCl.sub.4, HSiCl.sub.3 and H.sub.2 SiCl.sub.2, with ammonia at a high temperature and in a vapor phase. It is difficult to manufacture shaped articles, especially fibers, using this method because it directly yields a powdered product. In contrast, organopolysilazanes can also be spun into continuous fibers, the pyrolysis of which yields ceramic fibers.
Organopolysilazanes can also be shaped into films of various gauges and into massive molded articles. The organopolysilazanes can be used as binders for ceramic fiber or carbon fiber, and can also be used as sintering binders for porous ceramic articles.
However, difficulties are encountered in converting these organopolysilazanes readily and economically into a form of fibers or coatings that, after pyrolysis, yield ceramic products in the form of fibers, films, coatings of various gauges, and molded articles.
An attempt to solve this problem was made in U.S. Pat. No. 3,853,567. This patent discloses a process for the manufacture of shaped articles such as fibers comprising silicon carbide, silicon nitride or mixtures thereof with other ceramic products by first performing a thermal treatment of an organopolysilazane at a temperature between 200.degree. C. and 800.degree. C. The process obtains a meltable carbosilazane resin that can be melt-spun and then pyrolyzed at a temperature between 800.degree. C. and 2000.degree. C.
Although U.S. Pat. No. 3,853,567 represents a significant step forward, it has two disadvantages. First, it requires the thermal treatment to be conducted at a high temperature, such as 200.degree. C.-800.degree. C. Secondly, it requires working with a carbosilazane in melt form under anhydrous conditions and in an inert atmosphere. In addition, the weight yield of the ceramic is inadequate.
Japanese Patent Application Kokai No. 77/160,446 describes a process for the polymerization of organopolysilazanes of high molecular weight while using acidic earths as catalysts for the treatment of the organopolysilazanes. However, this process has the major disadvantage of requiring the solid catalyst to be separated off by filtration. This implies the use of a solvent for polymers that can reach high viscosities.